Yakov B. Zel’dovich (“Yasha” to intimates, “Ya.B.” to coworkers and students) was born in Minsk, then in the Soviet Union, now the capital of Belarus, and moved as an infant to Petrograd, which became Leningrad in 1924 and is now St. Petersburg. From age seventeen he worked at the Institute of Chemical Physics of the Academy of Sciences of the USSR in Leningrad (later in Moscow), where he started as a laboratory assistant and was quickly accepted as a scientist despite the lack of a bachelor’s degree. He later earned his doctorate at the Institute while working there. In his later years he was a member of the USSR Academy of Sciences and also a professor at Moscow State University, where he was the founding head of the Division of Relativistic Astrophysics at the Sternberg Astronomical Institute. He later headed the theoretical division of the Institute of Physical Problems. He made significant discoveries and wrote important books on problems of combustion and detonation. He worked on shock waves and gas dynamics and played a leading role in the development of Soviet nuclear and thermonuclear weapons. In the 1950s he turned to nuclear physics and the theory of elementary particles, and in the 1960s to astrophysics and cosmology. He worked on the dynamics of neutron emission during the formation of black holes, accretion onto black holes and neutron stars, the formation of galaxies and clusters, and the large scale structure of the universe. With Rashid Sunyaev he proposed what is known as the Sunyaev-Zel’dovich effect, an important method for determining the Hubble constant from the effect of gas in galaxy clusters on the microwave background radiation. He was a pioneer in attempts to relate particle physics to cosmology and to develop a quantum theory of gravity. He was also an important teacher and the leader of one of the world’s leading research groups in general relativity and cosmology. Note: His name is also spelled Zeldovich. The only correct spelling is in the Cyrillic alphabet: Яков Борисович Зельдович.